As I mentioned in my previous post, my “optimizations” of the multi-mode receiver code caused a sudden loss in performance.This was a big surprise because what I did was to replace two filters with only one, which I would expected to yield a performance gain and certainly not a loss. What happened at the same time was that the sample rate in the demodulators went from 50 ksps to 250 ksps and it was the responsibility of the demodulators to downsample this to 50 ksps. I suspected that this might have cause the increased CPU load and I have set up a simple experiment to confirm it.
gnuradio
AM/FM/SSB software receiver with Qt GUI
I have been a bit quiet over the last few weeks but don’t you worry, it is only because I have been busy and I can now present you what I have been tinkering with during the last few weeks: An AM, FM, SSB and CW receiver implemented using GNU Radio (python) and Qt graphical user interface.
NOAA 18 and 19 APT images Sunday, 17 Oct 2010
A few APT images received from NOAA 18 and NOAA 19 yesterday. THe setup I used was the very same that I have described earlier. Click on images to see full resolution and image details.
GNU Radio 3.3.0 on Mac OS X – USRP
I have now tried the USRP on Mac OS X using the MacPorts installation and I am happy to report that it works very well. Indeed, the USRP is really plug and play on OS X and there is no need to configure udev or anything like it is the case on e.g. Ubuntu Linux. The video below shows the FM receiver listening on the local APRS frequency.
GNU Radio 3.3.0 on Mac OS X
Few days ago Michael Dickens announced that the GNU Radio packages on MacPorts have now been updated to 3.3.0 and so I took this opportunity to try it. I didn’t have MacPorts installed so I had to start from scratch; however, installation was quite straightforward because the dependencies are resolved automatically. All I had to do was to download the latest MacPorts dmg and then execute the command
sudo port install gnuradio
then let it run overnight. It takes a long time since MacPorts builds everything from source. On my iMac it took more than 6 hours. Note that gnuradio is a meta packages that depends on all GNU Radio components.
An experiment with Theora and Ogg for DVB
Yesterday I have been testing the DVB setup using Theora encoded video in Ogg container instead of the H.264/MPEG-TS I have been using so far. Initial tests looked promising, but at the end the link was rather choppy and broken. On this first screen shot I am running the simulator (i.e. no USRP) with a … Read more
A different look at random noise
I was reading about the probability density function when I suddenly realised what the histogram sink in GNU Radio can be used for. I knew very well what a histogram is and how it used in e.g. physics, I just didn’t quite know what to use it for in a software radio.
Broken RFX1200 and more sensitivity measurements
I went to OZ7SAT today to do some measurements on the receiver boards. I wanted to see how the sensitivities compare to that of the WBX receiver that I have measured earlier using a CW signal and SSB receiver. The criteria was again to find the weakest signal that I could both hear and see on the spectrum scope and that I would be able to decode if it was a Morse code transmission. The limiting parameter is actually the spectrum scope, because I can hear tones much weaker than what is visible on the 512 channel FFT scope.
Simple SSB transmitter using complex bandpass filter
There are several ways to generate a single side band signal in a software radio and I am slowly exploring each and every one of them. For this first attempt I have decided to try using a basic amplitude modulation followed by a bandpass filter with complex taps that can select either the upper or the lower side bands.
Full duplex transceiver version of the DVB setup
This weekend I have been playing with a full duplex transceiver version of the simple DVB setup that allows to use only one computer and one USRP as a transmitter and receiver. By using separate daughterboards I can use one side to transmit and the other side to receive. Using two sets and two frequencies the transceiver can be used for two-way video conferencing over the air 🙂